Carbon nanotubes and nanocoils are expected as the charging materials and electron gun for the imaging devices. It is synthesized for carbon nanocoils with different diameters by the catalytic thermal decomposition of acetylene using iron-indium-tin-oxide catalysts. It is found that the turn-on voltage is decreased by decreasing the average diameter of the grown carbon nanocoils. The turn on voltage of as low as 30 V at the electrodes’ gap of 130 μm has been achieved when the coil diameter is decreased to 60 nm. The calculation for the concentration of the electric field on the coil surface has been performed using a finite element method. It is obtained that the strength of electric field around the top ring of a coil is increased with the decrease of the tubular diameter of the coil and has a similar value for that at the tip of a carbon nanotube, suggesting that the efficiency of the field emission from nanocoils would be higher than that from nanotubes. These results can explain the good stability of field emission from carbon nanocoils. Carbon nanotubes and nanocoils are expected as the charging materials and electron gun for the imaging devices. It is synthesized for carbon nanocoils with different diameters by the catalytic thermal decomposition of acetylene using iron-indium-tin-oxide catalysts. It is found that the turn -on voltage is decreased by decreasing the average diameter of the grown carbon nanocoils. The turn on voltage of as low as 30 V at the electrodes’ gap of 130 μm has been achieved when the coil diameter is decreased to 60 nm. The calculation for the concentration of the electric field on the coil surface has been performed using a finite element method. It is that that strength the electric field around the top ring of a coil is increased with the decrease of the tubular diameter of the coil and has a similar value for that at the tip of a carbon nanotube, suggesting that the efficiency of the field emission from nanocoils would be higher than that from nanotubes. These results can explain t he good stability of field emission from carbon nanocoils.